Ancient battlefields were inundated with colorful uniforms, tall easily visible hats festooned with tassles and feathers, ornate unit flags, horns, and all of these attention getting and vibrant vestments were simply ways for warriors to identify where they were on a battlefield, and where they were supposed to be. At the end of the 20th century long-range firearms and fully automatic weapons made it possible to level soldiers from extreme distances. Soon enough we began to see the precursors to camouflage. The British abandoned red uniforms and adopted khaki uniforms. Germans changed their uniforms from blue to gray. The French however had a different way of looking at it. A distinctly local and nationalist one: “Le Pantalon Rouge, c’est la France!” During the Battle of the Marne in 1914 the French marched into bright yellow cornfields in bright red trousers and jackets. Bullets whistled accurately into their ranks, easily seen, even through the fog and smoke of the battlefield. The following year a desaturated dark blue color graced the uniform of the French.
Sources: Wikipedia and Flickr